The comparison of pathogenesis of selected bunyaviruses and their RNA segment reassortment (reassortant) progeny viruses in mosquito vectors will be continued. The ability of cloned, defined RNA segment viruses to per os infect and to be transmitted by Aedes triseratus and other vectors will be determined and compared. Initial studies with LaCrosse and snowshoe hare and their reassortant viruses have demonstrated that when the m RNA segment is derived from the LaCrosse parent the ability of the virus to disseminate from the midgut and to be per os transmitted by Aedes triseratus is greatly increased. Subsequent studies will be directed to determination of anatomic or physiologic mechanisms accounting for these observations. Potential for ressortant virus formation in mosquitoes will also be studied. Since many bunyaviruses are known to be efficiently transovarially transmitted, the possibility of dual infection of vectors in nature is enhanced. Such dual infections could lead to ressortant virus generation.